You're not doing anything wrong, it just doesn't work you think it would... UC Surface "sees" the EarMix in the process of updating firmware, but that's it. It will never show up in use, because it's a network device with no external control. By default (reset of project, scene and patching) the mixer waits for the EarMix to accept AVB streams 1-8 and 9-16. This is also default setting for the EarMix itself. When mixer and EarMix are connected via Ethernet cable (direct connection) and the mixer is running, then the EarMix should be started and when the LED turns blue (red -> green -> blue), it is connected to the mixer via AVB. The only thing to do then is to check if the EarMix shows up in UC Surface (Settings -> Network) and maybe click on "Apply" to confirm AVB routing.
"Default" means that mixer channels 1 to 16 are routed to EarMix channels 1 to 16. If you want a different routing or add more channels or mixes, you have to follow a different approach. But try to get the default settings work first...
Hope this helps.